首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   38618篇
  免费   361篇
  国内免费   351篇
安全科学   1042篇
废物处理   1733篇
环保管理   4742篇
综合类   5662篇
基础理论   10117篇
环境理论   15篇
污染及防治   10577篇
评价与监测   2833篇
社会与环境   2368篇
灾害及防治   241篇
  2023年   197篇
  2022年   439篇
  2021年   453篇
  2020年   298篇
  2019年   371篇
  2018年   681篇
  2017年   699篇
  2016年   1045篇
  2015年   727篇
  2014年   1117篇
  2013年   3179篇
  2012年   1325篇
  2011年   1743篇
  2010年   1469篇
  2009年   1397篇
  2008年   1746篇
  2007年   1810篇
  2006年   1631篇
  2005年   1292篇
  2004年   1334篇
  2003年   1231篇
  2002年   1158篇
  2001年   1524篇
  2000年   1012篇
  1999年   648篇
  1998年   495篇
  1997年   438篇
  1996年   479篇
  1995年   506篇
  1994年   500篇
  1993年   435篇
  1992年   459篇
  1991年   409篇
  1990年   438篇
  1989年   420篇
  1988年   372篇
  1987年   322篇
  1986年   285篇
  1985年   287篇
  1984年   347篇
  1983年   326篇
  1982年   362篇
  1981年   291篇
  1980年   241篇
  1979年   287篇
  1978年   241篇
  1977年   212篇
  1975年   192篇
  1974年   193篇
  1972年   200篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
571.
One hundred and fifty-one women of advanced maternal age who underwent genetic termination of pregnancy (TOP) were studied for their reproductive behaviour and the type of procedure for prenatal diagnosis in a subsequent pregnancy. A total of 59 women (39 per cent) had a further pregnancy. In all continuing pregnancies prenatal diagnosis was performed, of which 75 per cent consisted of chorionic villus sampling (CVS). Reproductive behaviour following a genetic termination was negatively correlated with maternal age and parity. Both reproductive behaviour and the choice to undergo a diagnostic procedure in the next pregnancy were independent of the type of diagnostic procedure in the previous affected pregnancy.  相似文献   
572.
This paper, based on the autonomy concept, continues to investigate hierarchical forms and spatial structure of ecosystems. The former can lead to limits for the selection of the component parts of an ecosystem and a distinction between its endogenous and exogenous variables; and the latter can be lead to a hypothesis of the space of an ecosystem: the space of an ecosystem = its habitat area + supporting area + impact area, and two characteristics of ecosystems, space-overlapping and the area of ecosystem space, have been further studied referring to human activities.  相似文献   
573.
574.
The sinusoidal fetal heart rate pattern has been described in association with severe fetal anaemia, with fetal hypoxaemia, and with the administration of parenteral narcotics. Here, we report a case of decreased fetal movement in which a sinusoidal tracing was recorded. The sonographic diagnosis of a massive fetal intracranial haemorrhage was made. A non-interventive approach was taken and the fetus died soon after in utero. We review 28 previous cases in which the prenatal sonographic diagnosis of fetal intracranial haemorrhage was made, including the underlying maternal and fetal factors and neonatal outcomes. We propose that the sinusoidal tracing in this case was due to the intracranial bleed and suggest that fetal intracranial haemorrhage be considered in the sonographic evaluation of the fetus with a sinusoidal pattern.  相似文献   
575.
We report two cases of apparently balanced complex de novo chromosomal rearrangements (BCCR) detected prenatally at 17 weeks and 10 weeks of gestation, respectively. Chromosomes were studied using GTG-banding and fluorescent in situ hybridization (FISH). In one case four chromosomes and in the other case three chromosomes were involved in the rearrangements. One of the pregnancies was terminated and no external or internal abnormalities were detected at autopsy. The other pregnancy continued to term. Level III ultrasound examination showed no abnormalities. The child is now 3 years old and has neither congenital anomalies nor evidence of delayed psychomotor development.  相似文献   
576.
577.
We describe a patient with a significantly elevated serum alphafetoprotein (AFP) concentration at 17 weeks of gestation, who showed only a marginally increased amniotic fluid AFP and lacked the second rapidly migrating band of acetylcholinesterase electrophoresis. Ultrasound examination revealed an encephalocele and ventriculomegaly. Autopsy showed that the encephalocele was not covered by skin.  相似文献   
578.
579.
Reverse phase HPLC of radioactive globin chains has been compared to classical carboxy methyl cellulose chromatography for the prenatal diagnosis of β thalassaemia. The two methods correlated highly (r = 0.97 p < 0.0005) and provided an identical diagnosis for 40 fetal blood samples of fetuses homozygous or heterozygous for β thalassaemia. The HPLC procedure was much faster and required fewer biochemical steps (no globin preparation). It was at least as accurate and more sensitive than the classical chromatography. A single column can be used for 150 analyses and is always ready to be used. Last but not least it is much less expensive than CMC chromatography.  相似文献   
580.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号